1. Field of the Invention
The present invention relates to measures against light leakage in a telescopic lens barrel which is used for an imaging optical system, which retracts a lens group in a pattern and which extends the lens groups to a predetermined position in a usage pattern. More particularly, the invention relates to a lens barrel suitable for a zoom lens which relatively moves a plurality of lens groups to change a focal length.
2. Description of Related Art
In image pickup apparatuses such as digital cameras, as performance of image pickup lenses such as zoom lenses whose focal length can be changed is enhanced and in keeping with the trend towards downsizing as desired by users, so-called telescopic image pickup lenses having a lens barrel which is accommodated in an image pickup apparatus main body when the image pickup apparatus is not used for image pickup are increasing.
Users desire reduction not only in size but also in thickness. With this, it is important to reduce the thickness of the lens barrel in its retracted state as thin as possible.
A technique for satisfying the requirement of reduction of the image pickup apparatus in thickness include the telescopic structure in which the lens barrel is accommodated in the image pickup apparatus when the image pickup apparatus is not used for shooting. In the telescopic lens barrel of this kind, however, a distance between a plurality of lens holding frames which respectively hold the plurality of lens groups is shortened, thereby leading to interference between the lens holding frames and another member.
To resolve the interference, a notch or hole is formed in a portion of the lens holding frame which interferes with another member, thereby to form an opening, i.e., a through hole through which the lens holding frame pass.
As a result, light does not pass through the original optical path formed by the lens and a harmful light passing through the through hole of the lens holding frame, so that image deterioration such as flare is generated by the harmful light.
Techniques for resolving the harmful light passing through the through hole of such a lens holding frame are disclosed in Japanese Patent Applications Laid-open (JP-A) Nos. 2006-79070 and 2005-308843, and Japanese Utility Model Registration No. 2565022.
JP-A-2006-79070 describes a constitution in which an elastically deformable light shielding elastic tongue piece is fixed to a lens holding frame, and the light shielding elastic tongue piece comes into contact with an inner peripheral surface of an outer peripheral barrel, thereby shading the through hole portion.
JP-A-2005-308843 describes the following constitution. A wall of a lens holding frame having a notch is provided with a light shielding piece such that the light shielding piece can rock around an axis which is substantially in parallel to a plane intersecting with an optical axis perpendicularly. The light shielding piece is retracted substantially in parallel to the optical axis by a projection of the other lens holding frame in its retracted state. In the shooting state, the light shielding piece is returned to the light shielding state which is substantially in parallel to a plane intersecting with the optical axis perpendicularly by a biasing member.
Japanese Utility Model Registration No. 2565022 describes a constitution in which a light shielding member made of thin film light shielding sheet is provided, the light shielding member being formed at its outer peripheral edge with a large number of notches in the radial direction, thereby shading a gap of a slide fitting portion.
However, the constitution described in JP-A-2006-79070 has a problem in durability because the elastically deformable portion is pushed and bent. Further, it becomes a resistance against a relative movement between the lens holding frame and an outer peripheral barrel, which affects a driving force of the lens barrel.
According to the constitution described in JP-A-2005-308843, the light shielding piece is retracted substantially in parallel to the optical axis in the retracted state. Therefore, a size of the light shielding piece affects a size of the lens barrel in its retracted state, and for example, its thickness is increased.
If the constitution described in Japanese Utility Model Registration No. 2565022 is employed for the lens barrel of the present invention, a load is always applied to the light shielding sheet when the lens barrel is in its retracted state, and if the retracted state is maintained for a long time, the light shielding sheet is plastically deformed, which damages the light shielding in the shooting state.